1. Field of the Invention
The present invention relates to a method of manufacturing an organic electroluminescence (hereinafter, abbreviated as EL) display apparatus.
2. Description of the Related Art
Japanese Patent No. 3,250,561 discloses a method of manufacturing an organic EL display apparatus for performing so-called aging to suppress a change in luminance of the organic EL display apparatus with elapse of time. The aging is a treatment for applying a current between an anode and a cathode. According to the disclosed method, the aging for obtaining a curve of change in luminance with time, which is measured when an organic EL device is driven at a constant current, is first performed. Thereafter, the curve of change in luminance with time is analyzed to be divided into a component having a slowest luminance age-deterioration rate and other components. Then, the aging is conducted until a luminance becomes approximately equal to an initial value of the component having a slowest luminance age-deterioration rate.
Japanese Patent No. 3,552,317 discloses a method of manufacturing an organic EL display apparatus for aging an organic emission layer interposed between an anode and a cathode formed on a substrate at a current density 5 to 1000 times as large as a current density during the use. In addition to this method, there is also disclosed a method of manufacturing an organic EL display apparatus for aging an organic emission layer at a current density of 0.01 to 1 A/cm2.
Each of the above-mentioned related art references describes the invention for performing the aging by applying a prescribed current to the organic EL device to reduce a change in luminance of the organic EL device when a predetermined current density or a predetermined voltage is applied after the aging. However, when the aging is performed at the prescribed current, the luminance during or at the end of the aging sometimes differs from the maximum luminance during the use because the luminance of the organic EL device during the aging successively changes. In this case, the appropriate aging is not sometimes performed for the following reasons.
The organic EL device tends to have a higher rate of change (|dL/dt|) in luminance (L) per unit time as the luminance becomes higher. Therefore, when the luminance during the aging is lower than the luminance during the use, the rate of change (|dL/dt|) during the use becomes higher than the rate of change at the end of aging even if the rate of change (|dL/dt|) during the aging reaches a predetermined value. Accordingly, there is fear that the upper limit of the amount of change with elapse of time at the maximum luminance, which is demanded for the use, is not achieved.
On the other hand, when the luminance during the aging is higher than the luminance during the use, |dL/dt| tends to be lower than |dL/dt| at the end of the aging even if the rate of change (|dL/dt|) during the aging reaches a predetermined value. Therefore, there is fear that the aging is performed longer than needed to exceed the upper limit of the amount of change with elapse of time at the maximum luminance, which is demanded for the use.
As described above, when the aging is performed at a constant current applied to the organic EL device, the estimation of a change in |dL/dt| due to the aging at the maximum luminance during the use sometimes becomes difficult because the luminance of the organic EL device is not constant.
The organic EL device generally has a larger change (deterioration) in luminance per unit time as the luminance (L) becomes higher. Therefore, when the luminance used for the aging differs from the luminance during the use, the luminance during the actual use is not sometimes stabilized to be a predetermined amount or less even if the change in luminance per unit time is reduced to the predetermined amount or less. Therefore, when the luminance during the aging is lower than the luminance during the actual use, the completion of the aging cannot be determined because the change in luminance per unit time during the aging is larger than the change in luminance per unit time during the actual use.
In order to avoid the above-mentioned situation, it is necessary to set a luminance value for the aging larger than the maximum value of the luminance during the actual use. However, when the aging is performed at a constant current value, the luminance of the organic EL device is varied by the aging. Therefore, it is disadvantageously difficult to estimate an optimal luminance for aging in consideration of the change in luminance due to aging.